Reverted delist adaptor

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40377

scrapy/trunk/scrapy/contrib/adaptors/misc.py

@@ -63,12 +63,16 @@ def canonicalize_urls(value):
         return canonicalize_url(value)
     return ''
 
-def delist(value, join_delimiter=' '):
+class Delist(object):
     """
     Input: iterable with strings
     Output: unicode
     """
-    return join_delimiter.join(value)
+    def __init__(self, delimiter=' '):
+        self.delimiter = delimiter
+    
+    def __call__(self, value):
+        return self.delimiter.join(value)
 
 class Regex(object):
     """